1. Field of the Invention
The present invention refers to a method and a device for structuring photolithographic layers, particularly for microelectronics, microsystem technology, thin-film technology, the manufacture of flat screens, the direct exposure of semiconductor wafers in the manufacture of semiconductors and the structuring of masks and reticles for microlithographic applications.
2. Description of the Background Art
Exposure devices for the direct exposure of light-sensitive layers are already known in the prior art.
WO 93/09472 describes an exposure device comprising a light source and a pattern generator. The pattern generator includes an optical Schlieren system and an active matrix-addressable plane light modulator. In addition this known exposure device contains a movable positioning table on which a substrate to be exposed may be mounted. The light source used there is a pulsed laser with a pulse duration which is so short that picture fadings affecting the image quality do not occur when the positioning table carrying the substrate is moved continuously during the exposure of a single picture. In this way it is possible to achieve relatively high writing speeds.
WO 91/17483 and WO 93/09469 describe similar exposure devices for the direct exposure of light-sensitive layers, in which this exposure is also achieved using a plane light modulator.
The disadvantage of the exposure devices described above is that due to the size of the picture elements (pixels), in particular due to the width of the picture elements on the plane light modulator and because of the imaging scale of a projection optical system, a structure increment is fixed in advance and cannot be arbitarily reduced. A structure increment is the smallest amount by which a structure on the substrate to be illuminated can be enlarged or reduced.
In particular, there is a discrepancy between the theoretical structure resolution of a matrix-addressed plane light modulator of one or two pixels and the structure increment of one pixel since nearly all the technologies in a semiconductor process are based on a ratio of the structure increment to the minimum structure size of less than 1:10.
With the exposure devices known in the prior art and described above, the structure increment can only be reduced in a technologically or technically restricted framework by enlarging the imaging scale of the projection optical system or by reducing the width of the picture elements on the plane light modulator.
This leads in both cases to a considerable reduction in the writing speed of the system, which is proportional to the square of the product of the width of the picture element on the plane light modulator and the imaging scale.
A further disadvantage of these known devices is the defect sensitivity of these devices. Because of the size of the plane light modulators which are used, it is not normally possible to exclude defects on the plane light modulator, which means that a number of picture elements cannot be addressed or cannot be addressed completely.
WO 93/09472 solves this problem by ascertaining all the defective picture elements and treating them in such a way that they no longer refelect light. In this known device a structure is created by mutually overlapping partial pictures, so that it is assured that each part of the structure to be exposed is exposed at least once by a functional picture element. This overlapping of two neighbouring single pictures on the substrate leads to a reduction in the writing speed of this known device by a further factor of two.